Temperature-operated switch

ABSTRACT

A thermostat comprises a reed switch having a pair of normally open contacts, a barium-ferrite permanent magnet disposed parallel to the reed switch, and a manganese-zinc group ferrite member positioned proximate the permanent magnet to form a series circuit for the magnetic flux of the permanent magnet. The ferrite member exhibits a stauration magnetic flux density characteristic varying in response to temperature changes whereby the reed switch contacts are closed.

United States Patent 119 1' Kato et a1. .1451 July 31, 1973 [54] v TEMPERATURE-OPERATED SWITCH 3,295,081 12/1966 'Bowyer et al 335/208 [75] Inventors: Umaki Kato; MasanoriEndo; Katsuo FOREIGN PATENTS OR APPLICATIONS Kim", 3110f Yokohama, Japan 1,549,349 11/1968 France 335/146 [73] Assignee: Tohoku Metal Industries Limited,

Miyakpken, Japan Primary Examiner-Roy N. Envall, Jr. v Attorne'y-KurtKelman [22] Filed: May 18, 1971 1 [21] Appl. No.: 144,617 [57] ABSTRACT A thermostat comprises a reed switch having a pair of [52] [1.8. CI. 335/208- normally open contacts a barium-ferrite Parmiment [51] Int. Cl. .Q 1101b 37/58 magnet disposed Parauel the reed Swiich, and a 58 Field 01 Search 335/146, 208, 205 ganese'zinc 8 P fem: member PosifiOned P mate the permanent magnet to form a series circuit for 5 References Cited the magnetic flux of the permanent magnet. The ferrite UNITED STATES PATENTS member exhibits a stauration magnetic flux density characteristic varying in response to temperature l aga changes whereby the reed switch contacts are closed. 3,161,742 12/1964 Bagno 335/208 1 6 Claims, 15 Drawing Figures PAIENIEDJUm 1915 saw 1 0F 3 F lG.2b

TEMPERATURE F IGJ .:mzwn x3. 3.3.33

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S m E on N D F- NM E VmE N A K m m NT INU C KK N 7 T Om MAA D UMK T AL mmc A5 B F. l 3 E //m NW E m T AL MM X A changes in the temperature.

' tion, magnetic flux density (saturation induction) versus: 7

Temperature-operated switches using magnetic materials are known. Such switches are of the type in which the saturation flux density versus temperature characteristics of a magnetic substance areutilized to control the flux of a permanentmagnet .to cause opening and closing of the switch contacts in response to the strength or distribution of the magnetic flux. Other types of temperature operated switches which utilize phenomena, such as expansion, contraction, variations in electric resistance, or thermoelectric vpotentialsdeveloped by substances located at the, detecting portion of the switch, are also known.

Hitherto, it had been thought necessary to use ferrites for such temperaturesopetated switches. However, temperature-operatedswitches :usingferriteshave not been successful because ;a ferrite-is akind of ceramic, and thusdiffers largely, in :thermal expansion coefficient from the other-structural components ofthe switch; it is poor in its resistanceto heat-shoc,k;;it has a large thermal capacitygand it,is -poor--in thermal .conductivity. Further, such switches-suffer fromthe disadvantage that. it is impossible to 'makethe temperature,

at which they switch, variable.

The present invention has overcome-the foregoing disadvantages of the prior "artby zthe provision of a temperature-operated switch which is-constructed so that its contacts are opened and closed by the use of a' small amount of ferritematerial which has a preferential heat-response characteristic and a high resistance to heat-shock, and which permits adjustment of the switching temperature.

In the drawing,

FIG. 1 is a graph showing the saturation-flux density versus temperature of various magnetic substances;

FIGS. 2a and 2b are cross-sectional views of two prior art magnetic switches useful in understandingt-he operation of the instant invention;

FIGS. 3a and 3b are isometricviews of two embodiments of the invention having improved performance over the prior art structure disclosedin FIGS. 2a and 2b;

FIG. 4 is a cross-sectional view of another embodiment of the invention wherein the magnetic elements and the reed switch is offsetfrom the center of the .de-

vice;

FIGS. 5a and 5b are a magnetic flux graphand a cross-sectional view, respectively,;of yet 'another embodiment of the invention using anular magnetic members;

FIGS. 50 and 5d area magneticfluxgraph and crosssectional view respectively of another embodiment of the invention, difiering slightly :from that shown in FIGS. 5a and 5b,-

FIGS. 6a and 6b, 6c are across-sectional view and dimensional relationship graphs, respectively, of another embodiment of the invention; and 7 FlGS. 7a and '7b-;arecross-sectional views ofstill further embodiments of the invention.

Thepresent invention will be explained in detail with reference to the drawing. FIG. 1 shows several satura-j temperature characteristics in which curve 0 illustrates the characteristic of nickel-group alloys, such as an alloy consisting of Ni (32percent) and Fe (balance), whichare generally referred to as magnetic shunt alloys and-have'long been used .to compensate .for the thermal characteristic of permanent :magnets. Curve b illustrates the characteristic of ferrites, where the saturationrmagnetic flux density falls as the temperature rises and disappears when the temperature reaches the Curie point temperature To. The Curie point temperature of a ferrite can be-regulated freely by varying its composition. For instance, a substance whose Curie pointtemperature ranges from l,0.0 C to +300 C can easily be producedwfrom a Mn'Zn-group ferrite. The characteristic illustrated by curve 0 showsthe property of ,a-,material,.such .as a Fe-Rh-group powdered alloy or an Mn'CriSb'ln-group powdered alloy, .where the saturation magnetic flux density rises sharply at a certain temperature, due .to phase transformation. To compare theaforementionedmaterials, it should be observed that amagnetic .shuntalloy, is ametal and is, therefore,

superior-in heat-conductivity and workability to ferrites, but-it is virtually impossible to determine the Curie point temperature 'bylcontrolling the combination ratioof theelements in suchamaterial, thusresultmost preferable of all, in view of their sharp tempera- :ture characteristic but, because this type of material is a-powderedmetal substance, fragile and expensive, applications of this material are limited. Accordingly, from an-industrial point of view, the use of ferrites is the most-practicable solution.

FIG S.J2a;and 2b. are diagramatic views which explain the operation of a temperature-operated switchof the typein which apermane nt magnet and a magnetic substance (hereinafter referred to as a temperatureresponsive magnetic substance) are operatively combined,-the saturation mangetic flux density of the magnetic substance varying in response to temperature variations. 4

This temperature-operated switch is similar in construction to the well known magnetically operated switches (hereinafter referred to as reed switches) comprising a pair of elastic reedsmade of magnetic material and contacts thereon, which are normally open,

and which are closed when a magnetic flux passes through both reeds. However, unlike the prior art switches, the instant switch can be controlled in its .openingand closing operation by the ambient temperavture. The solidline depicted in thedrawing illustrates the flow .of magnetic flux when the temperatureshock.

responsive magnetic substance is a ferromagnetic material, and the dotted line illustrates the same when the temperature-responsive magnetic substance is a paramagnetic material.

In FIG. 2a, reeds 1 and 2 of the reed switch and temperature-responsive magnetic substances 3 and 4 are positioned so as to be in series with the magnetic flux of a permanent magnet 5 and, if magnetic substance 3 and 4 are ferromagnetic, the magnetic flux is conducted into the magnetic substance 3 and 4 and flows into the reeds, to move the reeds to the closed position. On the other hand, if the temperatureresponsive magnetic substances 3 and '4 are paramagnetic, the magnetic flux flows as shown by the dotted line so that the reeds l and 2 will be in a spaced apart position. If the magnetic substances are made of ferrite, the magnetic flux flowing through the reeds will decrease at elevated temperatures, so that this switch will act as a temperature-operated switch of the type in which contacts open at elevated temperatures.

In the embodiment shown in FIG. 2b, the reeds 6 and 7 of a reed switch, and a temperature-responsive magnetic substance 8, are positioned in parallel with a permanent magnet 9, so that, if magnetic substance 8 is ferromagnetic, the flux of the permanent magnet 9 exists within the substance 8, as shownby the solid line in the drawing, so that the contacts are in the spaced apart position. If the magnetic substance 8 is paramagnetic, the magnetic flux flows into the reeds 6 and 7 so that the contacts will be moved into the closed position. That is to say, if the magnetic substance 8 is made of ferrite, the contacts will close when the temperature rises and the saturation magnetic flux density of the ferrite decreases. Further, if the magnetic substance is made of a material which has a characteristic as shown in curve 0 (FIG. 1), the contacts will open when the temperature of the magnetic substance exceeds the phase transformation temperature. Since the characteristic of the flux density versus temperature of the magnetic substance is reversible, the operation of the contacts is reversed when the temperatute falls again.

Because the switch has a structure such that a pair of reeds are sealed in a glass container with inert gas, the switch is explosion-proof and can be used in applications where a conventional temperature-operated switch is not safe, for example, in an environment where there are explosive gases or dusts. Further, because the contacts have a snap action, a large number of switching operations can be expected if used with consideration of environmental conditions. Such a switch may prove unsatisfactory, however, because it includes glass which may break, or the operating characteristics, such as the switching temperature, may deviate from the expected figure due to differences in the thermal expansion coefficient of the glass and the magnetic substance, particularly when the device is subjected to elevated or low temperatures or to heat- In order to overcome the foregoing problem, the present invention uses a barium-ferrite magnet as the permanent magnet and a ferrite as the temperatureresponsive magnetic substance, assembles the former with the glass of the reed switch, and constructs all the important parts of the switch from ceramic. Thus, when the three elements noted above are bonded together by a heat-resistant synthetic resin, there will be no cracks formed in the glass, permanent magnet or temperaturenent magnet 11 is inserted in thehollow portion of a U- shaped temperature-responsive magnetic substance 12, both wing portions functioning as yokes to concentrate the magnetic flux of permanent magnet 11 when magnetic substance 12 is ferromagnetic. Therefore, the upper portion of the magnetic substance shunts the magnetic flux, the variation in magnetic flux acting to control the contacts of the reed switch 10 being quite large, and reliable operation can be expected. Further, the flux-shunting upper portion of the' magnetic substance isthe part of the device which directly senses temperature and thus can be miniaturized to increase the response of the device; It is possible to make the flux-shunting upper portion wider than the width of the permanent magnet 11 and correspondingly, to make the .same portion thinner, whereby the temperatureresponse is still further increased.

In FIG. 3b, the numeral 13 designates a reed switch, 14 designates a permanent magnet, and 15 designates a temperature-responsive magnetic substance. In this arrangement, the magnetic substance 15 surrounds the entire periphery of the side face of the magnet, so that the temperature-responsive magnetic substancehas an increased area, resulting in an increased response to temperature changes. The embodiments shown in FIG. 3a and FIG. 3b operate so that the switch contacts will be closed when the temperature-responsive magnetic substance behaves as if it were paramagnetic. It will be noted that, if the magnetic substance is made of a ferrite, the U-shaped or O-shaped magnetic substances can be molded integrally so that this device is readily mass-produceable.

The temperature-operated switch shown in FIG. 4 is of the type wherein the reed switch contacts are not positioned in the center portion of the switch assembly. The structure of this type of switch can generally be miniaturized, and the temperature-response may become rapid, depending upon its applications. As shown, a metal case 20 is immersed in fluid, the temperature of which is to be detected, and is mounted to the wall of a vessel, for example, by means of aflange 21. The numeral 22 designates one of the terminals of the switch, the other end being connected to the switch body. In this embodiment, the temperature operated switch, comprising a pair of reeds 23, a permanent magnet 24 and a temperature-responsive magnetic substance 25 is sealed in a metal case. Because the temperature detecting portion is proximate the far end of the device, there is little influence from the wall temperature, and in the case of fluid, the flow of the fluid increases as one moves away from the wall. Thus, this device has a good temperature response and operates as an accurate, temperature-operated switch. That is to say, in contrast to the usual type of switch in which the reeds are located at the center of a glass tube, in this embodiment the reeds are offset to one side'and the magnetic substance is correspondingly shifted towards the far endof the switch. i

FIGS. 5a and 5b show an embodiment of the invention wherein a ring-shaped magnetic substance is fitted around a reed switch and thus the magnetic substance has an increased surface area. This type ofswitch is characterized by an improved temperature response FIG. 5a illustrates the reed switch contact closing and temperature-responsive magnetic substance "54 sandwiched therebetweenyarranged in parallel with the reeds 50 and '51 of a reed switch. The magnetic subopening zones which appear when theaxial direction of I the reed switch is in alignment with the pole direction of the permanent magnet, and the contacts are moved relatively in the axial direction and in a vertical direction normal to the axial direction.lfFIG. 5a, the. zones designated 33, 34 and 35 arethe contact closing zones and 36 designates the contact opening zone. If arranged so that the permanent magnet 31 is fitted around the reed switch and positioned in the switch closing zone 36, thereed switch will be in the open position if the temperature-responsive magnetic substance 32 exhibits the property ofaparamagnetic material, and will be in the closedposition if the temperature-responsive magnetic substance 32-exhibits the property of a ferromagnetic material. That is, if the' magnetic substance 32 is madeof a ferrite, this temperature-operated switch operates in such a'manner that the contacts will be open if the device is subjected to elevated temperatures.

FIG. 5d shows a switch which operates in a manner inverse to theoperation of the device shown in FIG. 5b, that, is, the combination of a permanent magnet-41 and a temperature-responsive magnetic substance 42 which is located around an end portion of reed switch 40 closer to its end than the relationship shown in FIG. 5b. With reference to FIG. 50, if the temperatureresponsive magnetic substance 42 exhibitsthe property of paramagnetic material, only the permanent magnet 41, located in the contact closing zone 44, has any magnetic influence on the reed switch 40, so the contacts of the reed switch will be in the closed position. If the temperature-responsive magnetic substance 42 assumes thevproperty of a ferromagnetic material, the permanent magnet 41 and the temperature-responsive magnetic substance 42 serve substantially asa single permanent magnet, and the magnetic center of the equivalent single magnet shifts to the contact opening zone 46 and, thus, the contacts will open.

While the temperature-operated switch shown in FIG. 5b operates in the normal contact operation with conventional direction, the temperature-operated switch shown in FIG. 5d operates in the inverse manner and its operation is the same as that of the device shown in FIG. 2b. The device shown in FIG. 2b becomes large insize if it is designed in a cylindrical shape, but the temperature-operated switch shown in FIG. 5d is of smaller size and cylindrical and, thus, is

' easy to seal in a metal case, and the like.

to'manufacture than the switch shown in FIG. 5b and stance 54 is located so as to correspond in location to the-intermediateoverlapping portion of the reeds. In

- this embodiment, the magnetic flux appears as shown in the solid lines if the magnetic substance 54 exhibits the property of a ferromagnetic material. Thus, the

contacts will be in the closed position. On the other hand, if the magnetic substance 54 exhibits the prop- 'erty' of a paramagnetic material, the magnetic flux produced bype'rmanent 'magnets 52 and 53 is shunted by the respective reeds 50 and 51 of the reed switch, as shown by thedotted lines, so that the magnetic flux in the contact portion of the reeds disappears and the contacts will open. This switch can be constructed by mounting the combination of permanent magnets 52 and 53' and magnetic substance 54 about the central portion of the switch, so that this embodiment is easier gives a larger contact pressure due to the use of two permanent magnets. Thus, the contacts have a very long'life."

FIGS. 6b and 6c explain the dimensional relationship between permanent magnets 52, 53 and the magneticsubstance 54 forthe foregoing switch.

' FIG. 6b shows the case where the temperatureresponsive magnetic substance 54 issmaller in size than one of the permanent magnets 52 and 53, and FIG. 6c shows the case where the magnetic substance is larger than either. FIG. 6b, above the horizontal center line,

hibits the property of a paramagnetic material and therebelow is illustrated the case where the magnetic substanceexhibits the property of a ferromagnetic material. In this figure, the length, measured along the horizontal center line, represents the shift distance of either the permanent magnet or the temperatureresponsive magnetic substance in the axial direction. Zonesdesignated 55, 56, 57, and 58 represent the contactclosing zones which appear as the permanent magnet, and not the magnetic substance, which is moved in the axial direction. Contact closing zones 59, 60 and 61 are drawn, similarly to the above, by shifting the permanent'magnet, in combination with the temperatureresponsive ferromagnetic substance. Accordingly, when the temperature-responsive magnetic substance changes in property from a ferromagnetic material to a paramagnetic material, -the state of the contacts change from the condition shown below to that'shown ab'ove. That is, if the permanent magnets and the magnetic substance are located in the center portion of the switch, the contacts move from the closed position to the open position, within the limit'shown by the arrows.

In the case of FIG. 6c, where the temperatureresponsive magnetic substance is larger in size than the 'permanentmagnets, a closing zone 62 appears in the centerportion on the upper side and, if the permanent magnets and the temperature-responsive magnetic substance are located in the center portion of the switch, the contactsare kept closed so that, in order to get the intended type of operation, the contacts must be shifted slightly to the left or right. That is, in order to make good use of the advantagesof this type of temperature-op'erated'switch, it'is necessary to make the axial dimension of the temperature=responsive magnetic substance shorter than the length of the permanent magnet.

As described above, the switching temperature of these types of temperature-operated switches is defined by the operating properties of the reed switch, i.e. the strength of the retracting magnetic field, the characteristic of the saturation magnetic flux density versus temperature of the magnetic substance, the magnetic strength of the permanent magnet, the positional relationship between elements of the switch, and the like. Therefore, once the structural elements are bonded together, it was heretofore virtually impossible to vary any of the'foregoing parameters; To obviate the above problem, a ferromagnetic body other than the switching elements may be moved towards or spaced from the temperature-operated switch, or a magnetic field may be applied to the device by use of a coil.

In FIG. 7a, the numeral 71 designates a reed switch, 72 designates the combination of a permanent magnet and a temperature-responsive magnetic substance, and 73 designates a ferromagnetic substance to permit adjustment of the switching temperature. The ferromagnetic substance employed will permit adjustment of the switching temperature regardless of whether it is comprised of soft or hard ferromagnetic material. For example, if an iron piece approaches the switches shown in FIG. 2, the switching. temperature of the switch shown in FIG. 2a is lowered and that shown in FIG. 2b rises. In FIG. 7b, the numeral 74 designates a reed switch, 45 designates the combination of a ring-shaped permanent magnet and a temperature-responsive magnetic substance, and 56 designates a coilfor adjusting the switching temperature, the coil being wound coaxially with respect to element 45.-.The adjustment of theworking temperature can be effected by increasingor decreasing the supply of current to the coil.

One skilled in the art can make various modifications and changes to the illustrative embodiment shown, without departing from the spirit and scope of the invention.

We claim:

1. A temperature-operated switch, which comprises:

1. a reed switch having, in the absence of any external magnetic field, at least one pair of normally open contacts;

2. a barium-ferrite permanent magnet disposed substantially parallel to said reed switch; and

3. at least one manganese-zinc group ferrite member positioned proximate said permanent magnet such that a series circuit is formed for the magnetic flux of said magnet, said series circuit including said ferrite member and the reeds of said reed switch, said ferrite member exhibiting a saturation magnetic flux density characteristic which varies in response to changes in temperature, whereby the contacts of said reed switch are opened and closed by variations in the intensity and distribution ofthe magnet flux from said magnet caused by temperature induced variations in the magnetic characteristic of said ferrite member. 2. A temperature-operated switch, which comprises: 1. a reedswitch having, in the absence of any external magnetic field, at least one pair of normally open contacts; 2. a rectangular permanent magnet having four side faces, the permanent magnet being arranged sub stantially parallel to the reed switch; and

3. a magnetic member adjacent and surrounding the four side faces of the permanent magnet,

a. the magnetic member being disposed substantially parallel to the reed switch and forming therewith a series circuit for the magnetic flux of the permanent magnet, and I b. the magnetic member being comprised 'of a material exhibiting a saturation magnetic flux density characteristic varying in response to changes in temperature. 1

3. The temperature-operated switch of claim 2, wherein the magnetic member material is a manganesezinc group ferrite.

4. A temperature-operated switch, which comprises:

1. a reed switch having, in the absence of any external magnetic field, at least one pair of'nor'mally open contacts; t

2. a permanent magnet arranged substantially parallel to the reed switch;

3. a magnetic member positioned proximatethe permanent magnet and forming therewith a series circuit for the magnetic flux of the permanent magnet, the series circuit including the magnetic memher and thereeds of the switch,

a. the magnetic member being comprised of a material exhibiting a saturation magnetic flux density characteristic varying in response to changes in temperature whereby the contacts of the reed switch are opened and closed by variations in the intensity and distribution of the magnetic'flux from the permanent magnet caused by temperature induced variations in the characteristic of the magnetic member; 7

4. an electromagnetic coil mounted adjacent the magnetic member and arranged, upon energization, to alter the saturation magnetic flux density characteristic of the magnetic member. whereby the temperature at which the switch operates may be adjusted; and a 5. means for, energizing the coil to establish an electromagnetic field therein.

5. The temperature-operated switch of claim 4,

wherein the permanent magnet and magnetic'member ll l l i 

2. a barium-ferrite permanent magnet disposed substantially parallel to said reed switch; and
 2. A temperature-operated switch, which comprises:
 2. a rectangular permanent magnet having four side faces, the permanent magnet being arranged substantially parallel to the reed switch; and
 2. a permanent magnet arranged substantially parallel to the reed switch;
 3. a magnetic member positioned proximate the permanent magnet and forming therewith a series circuit for the magnetic flux of the permanent magnet, the series circuit including the magnetic member and the reeds of the switch, a. the magnetic member being comprised of a material exhibiting a saturation magnetic flux density characteristic varying in response to changes in temperature whereby the contacts of the reed switch are opened and closed by variations in the intensity and distribution of the magnetic flux from the permanent magnet caused by temperature induced variations in the characteristic of the magnetic member;
 3. a magnetic member adjacent and surrounding the four side faces of the permanent magnet, a. the magnetic member being disposed substantially parallel to the reed switch and forming therewith a series circuit for the magnetic flux of the permanent magnet, and b. the magnetic member being comprised of a material exhibiting a saturation magnetic flux density characteristic varying in response to changes in temperature.
 3. The temperature-operated switch of claim 2, wherein the magnetic member material is a manganese-zinc group ferrite.
 3. at least one manganese-zinc group ferrite member positioned proximate said permanent magnet such that a series circuit is formed for the magnetic flux of said magnet, said series circuit including said ferrite member and the reeds of said reed switch, said ferrite member exhibiting a saturation magnetic flux density characteristic which varies in response to changes in temperature, whereby the contacts of said reed switch are opened and closed by variations in the intensity and distribution of the magnet flux from said magnet caused by temperature induced variations in the magnetic characteristic of said ferrite member.
 4. A temperature-operated switch, which comprises:
 4. an electromagnetic coil mounted adjacent the magnetic member and arranged, upon energization, to alter the saturation magnetic flux density characteristic of the magnetic member whereby the temperature at which the switch operates may be adjusted; and
 5. means for energizing the coil to establish an electromagnetic field therein.
 5. The temperature-operated switch of claim 4, wherein the permanent magnet and magnetic member are ring-shaped and coaxially surround the reed switch and the electromagnetic coil is coaxial with the permanent magnet and magnetic member.
 6. The temperature-operated switch of claim 4, wherein the magnetic member material is a manganese-zinc group ferrite. 